Methods of reducing corrosion of materials, methods of protecting aluminum within aluminum-comprising layers from electrochemical degradation during semiconductor processing methods of forming aluminum-comprising lines

ABSTRACT

In one aspect, the invention includes a semiconductor processing method of reducing corrosion of a material, comprising exposing the material to a liquid solution comprising at least about 5% (by atomic percent) of an oxygen-comprising oxidant to form an oxide layer over the material. In another aspect, the invention includes a semiconductor processing method of forming an aluminum-comprising line within a layer of material, comprising: a) forming a layer of material over a semiconductive substrate; b) forming trenches within the layer of material; c) forming an aluminum-comprising layer within the trenches and over the layer of material; d) planarizing the aluminum-comprising layer to form aluminum-comprising lines within the material, the planarizing comprising abrading a portion of the aluminum-comprising layer with a first fluid, the first fluid comprising a slurry; and e) displacing the slurry with a second fluid comprising at least about 5% (by atomic percent) of ozone.

TECHNICAL FIELD

The invention pertains to semiconductor processing methods of reducingcorrosion of materials. The invention has particular application tomethods of forming aluminum-comprising lines, and to aluminum-comprisinglines.

BACKGROUND OF THE INVENTION

Corrodible materials are frequently utilized in integrated circuitryformed on semiconductive wafers. In the context of this disclosure, theterm "corrodible material" refers to a material that can undergoelectrochemical degradation during semiconductor fabrication processes.An example corrodible material is an aluminum-comprising material.Aluminum-comprising materials can, for example, consist essentially ofelemental aluminum, or can comprise an alloy, such as aluminum/copper.Aluminum-comprising materials are utilized in semiconductor applicationsas, for example, circuit components or conductive interconnects forelectrically connecting circuit components.

A method of forming aluminum-comprising conductive interconnects is adamascene method. In a damascene method, a pattern of trenches is formedwithin an insulative material. An aluminum-comprising layer is thenformed over the insulating material and within the trenches. Thealuminum-comprising material is subsequently planarized to removeportions of the material that are not within trenches.

The planarization typically comprises chemical-mechanical polishingutilizing a polishing pad to rub an abrasive slurry against thealuminum-comprising layer. Typically, the slurry comprises an aluminumoxide grit within an aqueous carrier solution. The slurry can have a pHof, for example, from about 2.5 to about 4.0. Example slurries areEP-A5655 (sold by Cabot), and XVS-6902 (sold by Rodel). In alternativeprocesses, a polishing pad is rubbed directly on an aluminum-comprisinglayer to abrade the layer. In such alternative processes, a liquid istypically provided over the aluminum-comprising layer during theabrading, but the liquid may not comprise a slurry. A prior art slurrypolishing process is described with reference to FIG. 1.

In step "A" of the FIG. 1 process a surface of a wafer is polished witha slurry. In the example process described herein, the polishing isutilized to abrade an aluminum-comprising material. Polishing of analuminum-comprising material can, for example, be incorporated into adamascene process.

After polishing of the aluminum-comprising layer, the slurry isdisplaced with deionized (DI) water (step "B" of the FIG. 1 process).The DI water is flushed between the polishing pad and the layer, withthe polishing pad typically continuing to spin relative to the surfaceduring such flushing. However, the DI water does not comprise a grit, soabrasion of the aluminum-comprising layer is substantially reduced asthe DI water displaces the slurry. The DI water can comprise a smallamount (10 to 20 ppm, or less than 0.01% (by atomic percent)) of ozonedue to atmospheric ozone diffusing into the water. The DI water can alsocomprise a small amount (less than 0.1%) of carbon dioxide and/orcarbonic acid due to diffusion of atmospheric carbon dioxide into thewater.

After the slurry is displaced, the polishing pad is separated from thewafer, and the wafer is transferred to an unload bath (step "C" of theFIG. 1 process). The unload bath contains deionized water, and keeps asurface of the wafer wet as remaining wafers in a cassette are polished.Typically, a cassette will contain at least twenty-five wafers, and thewafers are polished one or two at a time. Polished wafers are kept wetas other wafers in a cassette are polished because otherwise gritremaining on the wafers from the polishing process can dry and becomedifficult to remove. The DI water in the unload bath has a pH of atleast 7. As the wafers are transferred to the unload bath, they arepreferably sprayed with water to alleviate drying of slurry granules onthe wafers during the transfer.

After the wafers of a cassette are transferred to an unload bath, thewafers are transferred to a scrubber to further clean polishing gritfrom the wafer surfaces (step "D" of the FIG. 1 process). The scrubbercomprises a load station were the wafers are kept prior to beingscrubbed. The wafers are preferably sprayed with DI water as they arekept in the load station to alleviate grit drying on the wafers. Thewafers are then scrubbed to remove residual grit on the wafer surfaces.The scrubbing can comprise mechanically brushing grit from a wafersurface while immersing the wafer surface in a liquid. The liquid cancomprise, for example, water buffered with citric acid andtetramethylammonium hydroxide (TMAH) to maintain a pH of liquid withinthe scrubber to below 7. Such low pH liquid can assist in removing gritparticles from the wafer.

After the grit on the wafer is removed with the scrubber, the wafer istransferred to a location where it is spun dry (step "E" of the FIG. 1process).

A difficulty which can occur during the processing sequence describedwith reference to FIG. 1 is corrosion of a polished aluminum-comprisingmaterial. The corrosion can result in a loss of some or all of thealuminum-comprising material that is intended to remain on the waferafter the polishing process. If a relatively small amount of thematerial is lost, pits can occur within the aluminum-comprisingmaterial. If a larger amount of the material is lost, large crevices canbe formed within the material.

Corrosion of an aluminum-comprising material can adversely affectphysical properties of conductive lines formed from thealuminum-comprising material. For instance, conductance and strength ofthe aluminum-comprising material can be adversely affected. Also,pitting or crevice formation can decrease a surface planarity of apolished aluminum-comprising layer. As high surface planarity isfrequently desirable for subsequent process steps, a decrease in surfaceplanarity can adversely affect downstream fabrication processesutilizing the corroded aluminum-comprising layer. It would be desirableto develop alternative methods of processing aluminum-comprising layerswherein the above-described corrosion is avoided or at least reduced.More generally, it would be desirable to develop semiconductorprocessing methods which alleviate corrosion of processed materials.

SUMMARY OF THE INVENTION

In one aspect, the invention encompasses a semiconductor processingmethod of reducing corrosion of a material. The material is exposed to aliquid solution comprising at least about 5% (by atomic percent) of anoxygen-comprising oxidant to form an oxide layer over the material.

In another aspect, the invention encompasses a semiconductor processingmethod of reducing a thickness of an aluminum-comprising layer. Aportion of an aluminum-comprising layer is abraded with a first fluidcomprising a slurry having a polishing grit. The first fluid isdisplaced with a second fluid comprising at least about 5% (by atomicpercent) of an oxygen-comprising oxidant.

In yet another aspect, the invention encompasses a semiconductorprocessing method of forming an aluminum-comprising line within a layerof material. A layer of material is formed over a semiconductivesubstrate. Trenches are formed within the layer of material. Analuminum-comprising layer is formed within the trenches and over thelayer of material. The aluminum-comprising layer is planarized to formaluminum-comprising lines within the material. The planarizing comprisesabrading a portion of the aluminum-comprising layer with a first fluidcomprising a slurry. The slurry is displaced with a second fluidcomprising at least about 5% (by atomic percent) of ozone.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a flow chart view of a prior art semiconductor waferfabrication process.

FIG. 2 is a diagrammatic, fragmentary, cross-sectional view of asemiconductor wafer fragment at a preliminary step of a method of thepresent invention.

FIG. 3 is a view of the FIG. 2 wafer fragment shown at a processing stepsubsequent to that of FIG. 2.

FIG. 4 is a view of the FIG. 1 wafer fragment shown at a processing stepsubsequent to that of FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws "to promote the progressof science and useful arts" (Article 1, Section 8).

An exemplary method of the present invention is described with referenceto FIGS. 2-4. Referring to FIG. 2, a semiconductive wafer fragment 10comprises a substrate 12 and a dielectric (i.e. electrically insulative)material 14 overlying substrate 12. Substrate 12 can comprise, forexample, a monocrystalline silicon wafer lightly doped with a p-typeconductivity-enhancing dopant. To aid in interpretation of the claimsthat follow, the term "semiconductive substrate" is defined to mean anyconstruction comprising semiconductive material, including, but notlimited to, bulk semiconductive materials such as a semiconductive wafer(either alone or in assemblies comprising other materials thereon), andsemiconductive material layers (either alone or in assemblies comprisingother materials). The term "substrate" refers to any supportingstructure, including, but not limited to, the semiconductive substratesdescribed above.

Dielectric material 14 can comprise, for example, silicon dioxide orborophosphosilicate glass (BPSG). Trenches 16 are formed withindielectric material 14. Trenches 16 define a pattern for formation ofone or more aluminum-comprising lines.

Referring to FIG. 3, an aluminum-comprising layer 18 is provided overdielectric material 14 and within openings 16. The aluminum withinaluminum-comprising layer 18 can be in the form of, for example,elemental aluminum or an aluminum/copper alloy. If aluminum-comprisinglayer 18 comprises an aluminum/copper alloy, the copper can be present,for example, in a concentration of from about 0.25 to about 2.5 weightpercent.

Referring to FIG. 4, aluminum-comprising layer 18 is planarized toremove portions of layer 18 from over substrate 14 while leaving otherportions of layer 18 remaining within openings 16. The portions ofaluminum-comprising layer 18 remaining within openings 16 comprise oneor more conductive lines 20. The planarization of aluminum-comprisinglayer 18 (FIG. 2) can comprise chemical-mechanical polishing utilizing afirst fluid that comprises a slurry, or utilizing an abrasive polishingpad without a slurry. If the first fluid comprises a slurry, it cancomprise, for example, a slurry of the type discussed above in the"Background" section of this disclosure.

After layer 18 is planarized, a slurry can be displaced from overinsulative material 14 with a second fluid. The second fluid ispreferably a liquid, and preferably does not comprise grit. Mostpreferably, the second fluid is a liquid solution comprising at least 5%(by atomic percent) of an oxygen-comprising oxidant. For purposes ofinterpreting this disclosure and the claims that follow, the term"fluid" encompasses liquids and slurries, and the term "liquid" canrefer to a liquid portion of a slurry unless specified otherwise. Thepreferred fluid for displacing a slurry is a liquid which is not withina slurry.

The oxygen-comprising oxidant can comprise, for example, O₃ (ozone), orH₂ O₂ (hydrogen peroxide). Preferably, the oxygen-comprising oxidantcomprises ozone, and more preferably, the oxygen-comprising oxidantconsists essentially of ozone. The oxygen-comprising oxidant can bepresent in the second fluid to, for example, a concentration of at leastabout 10% (by atomic percent), a concentration of at least about 50% (byatomic percent), or a concentration of from about 10% (by atomicpercent) to about 50% (by atomic percent).

The oxygen-comprising oxidant oxidizes an upper surface of planarizedaluminum layer 18 to form a protective layer of aluminum oxide over thealuminum within layer 18. Such protective layer can alleviate corrosionof aluminum underlying the protective layer to avoid loss of aluminumfrom within layer 18. Thus, the aluminum oxide over layer 18 canalleviate corrosion of aluminum within layer 18, and can therebyalleviate corrosion-induced defects such as, for example, pit or creviceformation.

The fluid utilized to displace the polishing slurry (i.e., the secondfluid) can have a pH of at least 7, or less than 7. In some embodiments,it is preferred for the fluid to have a pH of less than 7, as suchacidic pH can reduce corrosion of an aluminum-comprising layer relativeto the corrosion which occurs when higher pH fluids are utilized.Specifically, it is found that electrochemical degradation can be amechanism whereby aluminum-comprising layers are corroded, and that arate of electrochemical degradation can be decreased by utilizing aliquid having a pH of less than 7. It is observed that corrosion ofpolished aluminum-comprising layers rinsed with prior artwater-comprising liquids generally occurs after a polishing slurry isremoved from the layer, rather than while the polishing slurry is incontact with the layer. Such observation is consistent with a mechanismwhereby the corrosion is caused by electrochemical degradation enhancedby a water-comprising liquid provided to displace slurry from thealuminum-comprising layer. It is also observed that if awater-comprising liquid having a pH of less than 7 is utilized to removepolishing slurry from an aluminum-comprising layer, corrosion of thelayer can be reduced relative to prior art methods of removing slurryfrom aluminum-comprising layers with solutions having pH's of at least7.0. This observation is also consistent with a mechanism whereincorrosion of aluminum-comprising layers is due to electrochemicaldegradation enhanced by basic solutions. Although a mechanism ofelectrochemical degradation induced corrosion is presented herein, it isto be understood that the present invention is intended to be limitedonly by the claims that follow, and not by any particular mechanism.

Methods for decreasing the pH of a solution can include, for example,incorporating one or more acids within the solution. Unless specifiedotherwise, the term "acid" is utilized herein to refer to bothprotonated and unprotonated forms of acidic material. The acid caneither be a strong acid (i.e., an acid having a pk_(a) of less than 2)or a weak acid (i.e., an acid having a pk_(a) of greater than or equalto 2).

An example acid for utilization in the present invention is citric acid.If citric acid is utilized in a method of the present invention, it ispreferably utilized in combination with a base (such as, for example,tetramethylammonium hydroxide (TMAH)) to form a buffered solution havinga pH of from about 2 to about 6.5, more preferably from about 4.5 toabout 6.5, and yet more preferably of from about 5 to about 5.5. Ascitric acid has one pk_(a) at about 4.8 and another at about 6.4, it canform a good buffer in the preferred range of from about 2 to about 6.5.TMAH is a preferred base because TMAH is known in the art to beparticularly effective for removal of aluminum oxide grit. An examplewater-comprising liquid of the present invention can be formed by mixing190 ml. of 10% (by atomic percent) citric acid, with 60 ml. of 25% (byatomic percent) TMAH and 5 gallons of water. Preferably, the ratio of10% citric acid to 25% TMAH is at least 3:1 (forming a ratio of citricacid to TMAH within the water-comprising liquid of greater than about1.25) to ensure that a pH of the liquid is below about 6.5.

Another example acid for utilization in the present invention iscarbonic acid. Carbonic acid has a pk_(a) of about 6.4, and thereforecan be an effective buffer within the preferred pH range of from about2.0 to about 6.5. Also, carbonic acid can be relatively easily added toa water-comprising liquid, by, for example, bubbling gaseous carbondioxide through the water-comprising liquid. The carbonic acid solutionpreferably comprises at least 10% (by atomic percent) of carbon dioxidederivatives (i.e. CO₂, H₂ CO₃, and HCO₃ --), more preferably comprises40% (by atomic percent) of CO₂ derivatives, and most preferablycomprises 50% (by atomic percent) of CO₂ derivatives.

In accordance with the present invention, the fluids described withreference to steps "B"-"D" of the prior art processing sequence of FIG.1 are preferably replaced with solutions comprising an oxygen-comprisingoxidant and/or a pH of less than 7. Specifically, the unload bathdescribed with reference to step "C" of FIG. 1 preferably comprises aliquid having a pH of less than 7. Preferred liquids are liquidscomprising either citric acid, or a mixture of citric acid and TMAH. Ifa liquid utilized in the unload bath comprise citric acid without TMAH,it preferably comprises a pH of from about 3 to about 3.5. If the liquidcomprises a mixture of TMAH and citric acid, it preferably comprises apH of from about 5 to about 5.5. The bath can also comprise at least 10%(by atomic percent) of ozone, at least 50% (by atomic percent) of ozone,or from about 10% (by atomic percent) to about 50% (by atomic percent)of ozone.

Also in accordance with the present invention, the scrubber describedwith reference to Step "D" of FIG. 1 preferably comprises a liquidcomprising a pH of less than 7. Preferred liquids are the citric acid,or citric acid/TMAH comprising liquids described above as preferredliquids for the unload bath of step "C" of FIG. 1. Further, thesolutions utilized to wet a wafer surface during transfer of a waferbetween a polishing apparatus and an unload bath (for instance, thetransfer between steps "B" and "C" of the process shown in FIG. 1), andin the load station of a scrubber preferably comprise water solutionshaving pHs of less than 7. A preferred water solution is a solutioncomprising carbon dioxide derivatives and water, and is not a slurry.Such solution preferably comprises at least 10% (by atomic percent) ofcarbon dioxide derivatives. Other example solutions comprise at leastabout 40% (by atomic percent) of carbon dioxide derivatives, and atleast 50% (by atomic percent) of carbon dioxide derivatives. Anotherpreferred solution is a solution comprising ozone and water.

In a most preferred process, an unload bath (such as that described withreference to step "C" of the FIG. 1 process) comprises citric acid/TMAHand a pH of less than 7, a scrubber (such as that described withreference to step "D" of the FIG. 1 process) comprises citric acid/TMAHand a pH of less than 7, and a rinse water (such as that described asutilized between steps "B" and "C" of the FIG. 1 process comprises asolution consisting essentially of water and ozone, with the ozone beingpresent to a concentration of at least about 5% (by atomic percent).Also in a most preferred process, a rinse water described as utilized inthe load station of the step "D" scrubber of the FIG. 1 processcomprises a solution consisting essentially of water and carbon dioxidederivatives, with the derivatives being present to a concentration of atleast about 10% (by atomic percent).

It is to be understood that, although the invention is described abovewith reference to application to aluminum-comprising materials, theinvention extends to other materials. The invention can, for example, beutilized for alleviating corrosion of any materials which are subject toelectrochemical degradation, and which can be protected from suchdegradation forming a thin oxide layer at a surface of the material, orby reducing a pH of a fluid to which the material is exposed.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

What is claimed is:
 1. A semiconductor processing method of processing an aluminum-comprising layer, comprising:forming an aluminum-comprising layer over a substrate; polishing the aluminum-comprising layer, the polishing comprising contacting at least a portion of the aluminum-comprising layer with a first fluid comprising a slurry; displacing the slurry with a second fluid comprising at least about 5% (by atomic percent) of an oxygen-comprising oxidant; and after the displacing, immersing the aluminum-comprising layer in a bath of a third fluid, the third fluid comprising water and a pH of less than 7.0.
 2. The method of claim 1 further comprising:after the displacing and before the immersing, rinsing the aluminum-comprising layer with a liquid, the liquid comprising a pH of less than 7.0.
 3. The method of claim 1 further comprising:after the displacing and before the immersing, rinsing the aluminum-comprising layer with a liquid, the liquid comprising water and at least about 5% (by atomic percent) ozone.
 4. The method of claim 1 further comprising:after the displacing and before the immersing, rinsing the aluminum-comprising layer with a first liquid, the first liquid comprising water and at least about 5% (by atomic percent) of ozone; after the immersing, transferring the substrate to a scrubber, the substrate being rinsed with a second liquid before utilizing the scrubber to scrub the substrate; and utilizing the scrubber to scrub the substrate, the scrubbing comprising exposing the substrate to a third liquid.
 5. The method of claim 4 wherein the first and second liquids are identical in composition.
 6. The method of claim 4 wherein the third liquid has a pH of less than 7.0.
 7. The method of claim 1 wherein the second fluid consists essentially of water and the oxygen-comprising oxidant.
 8. The method of claim 1 wherein the oxygen-comprising oxidant comprises O₃.
 9. The method of claim 1 wherein the oxygen-comprising oxidant consists essentially of O₃.
 10. The method of claim 1 wherein a difference between the first and second fluids is that the second fluid does not comprise a slurry.
 11. The method of claim 1 wherein the third fluid comprises a pH of from about 2.0 to about 6.5.
 12. The method of claim 1 wherein the third fluid comprises a pH of from about 5.0 to about 5.5.
 13. The method of claim 1 wherein the third fluid comprises a buffering component.
 14. The method of claim 1 wherein the third fluid comprises citric acid.
 15. The method of claim 1 wherein the third fluid comprises citric acid and TMAH.
 16. The method of claim 5 wherein the third fluid comprises at least 10% carbon dioxide derivatives (by atomic percent). 